The present invention is directed generally to photoresponsive, or photoconductive imaging members, and more specifically to photoconductive imaging members comprised of certain resin binders. In embodiments, the present invention is directed to an imaging member comprised of a supporting substrate, a photogenerating layer in contact therewith, and a charge, especially hole, transport layer comprised of transport molecules dispersed in improved binders of, for example, copolymers and diblock copolymers of styrene and alkyl methacrylates, styrene aryl methacrylates, styrene diene copolymers or substituted alphamethyl-styrene and substituted styrene, and vinyl polymers. The resin binders in embodiments are comprised of block copolymers of styrene with alkyl methacrylates such as benzylmethacrylates and cyclohexylmethacrylates, styrene arylmethacrylates such as styrene phenyl methacrylate, styrene diene copolymers such as styrene isoprene copolymers or substituted poly(alpha-methylstyrene) such as poly(p-isopropyl alpha-methyl styrene), and substituted polystyrenes such as poly(alpha-methylstyrene) and vinyl polymers such as poly(vinyl toluene) poly(p-isopropyl alpha-methyl styrene) and poly(vinyl benzyl chloride) and the like. With the binders of the present invention, toxic solvents, such as chlorinated solvents like dichloromethane; can be avoided when preparing the resulting imaging members. Moreover, the imaging members with the binders of the present invention are electrically and environmentally stable, possess excellent mechanical and xerographic cycling properties, for example increases in background and residual potentials of only 10 volts in 1,000 imaging cycles enabling their use for extended imaging cycles of, for example, 500,000. Also, the imaging members of the present invention can be rendered sensitive to wavelengths of from about 400, especially 450 to about 800 nanometers, that is from the visible region to the near infrared wavelength region of the light spectrum, and these imaging members in many instances possess excellent electricals, and outstanding time zero electricals, such as a dark decay of -30 volts/second, and E.sub.1/2 of about 1.5 ergs/cm.sup.2 at 790 nanometers, thus enabling use thereof in imaging systems with high speeds, for example exceeding 70 CPM, and have excellent cycling characteristics. In embodiments thereof, the imaging members of the present invention generally possess lower dark decay characteristics as illustrated herein.
Photoresponsive and photoconductive imaging members are known, such as those comprised of a homogeneous layer of a single material such as vitreous selenium, or composite layered devices containing a dispersion of a photoconductive composition. An example of a composite xerographic photoconductive member is described in U.S. Pat. No. 3,121,006, which discloses finely divided particles of a photoconductive inorganic compound dispersed in an electrically insulating organic resin binder.
Photoreceptor materials comprising inorganic or organic materials wherein the charge generating and charge transport functions are performed by discrete contiguous layers are also known. Additionally, layered photoreceptor members are disclosed in the prior art, including photoreceptors having an overcoat layer of an electrically insulating polymeric material. Other layered photoresponsive devices have been disclosed, including those comprising separate photogenerating layers and charge transport layers as described in U.S. Pat. No. 4,265,990, the disclosure of which is totally incorporated herein by reference. Photoresponsive materials containing a hole injecting layer overcoated with a hole transport layer, followed by an overcoating of a photogenerating layer, and a top coating of an insulating organic resin are disclosed in U.S. Pat. No. 4,251,612, the disclosure of which is totally incorporated herein by reference. Examples of photogenerating layers disclosed in these patents include trigonal selenium and phthalocyanines, while examples of transport layers include certain aryl diamines as illustrated therein. Examples of binders include polycarbonates and polyesters.
Examples of the highly insulating and transparent resinous components or inactive binder resinous material for the transport layer include materials such as those described in U.S. Pat. No. 3,121,006, the disclosure of which is totally incorporated herein by reference. Specific examples of suitable organic resinous materials include polycarbonates, acrylate polymers, vinyl polymers, cellulose polymers, polyesters, polysiloxanes, polyamides, polyurethanes, polystyrenes, and epoxies as well as block, random or alternating copolymers thereof. Preferred electrically inactive binder materials are polycarbonate resins having a molecular weight of from about 20,000 to about 100,000 with a molecular weight in the range of from about 50,000 to about 100,000 being particularly preferred. Generally, the resinous binder contains from about 5 to about 90 percent by weight of the active material corresponding to the foregoing formula, and preferably from about 20 percent to about 75 percent of this material. In methods known for the preparation of imaging members containing polycarbonate resins as inactive binder materials by web coating and dip coating processes, solvents like dichloromethane and chlorobenzene are used. Similar binder materials may be selected for the photogenerating layer, including polyesters, polyvinyl butyrals, polyvinylcarbazole, polycarbonates, polyvinyl formals, poly(vinylacetals) and the like, reference U.S. Pat. No. 3,121,006, the disclosure of which is totally incorporated herein by reference. There is an increasing concern about the use of chlorinated solvents like dichloromethane in these processes and there are indications that future governmental regulations will require the elimination and or reduction of chlorinated solvent emissions. There is a need to identify less harmful polymer/solvent systems that are compatible with the charge transporting materials so that alternate photoreceptor manufacturing processes can be developed. In addition, there is a need to improve the mechanical properties of the photoreceptors.
U.S. Pat. No. 4,713,307, the disclosure of which is hereby totally incorporated by reference, also discloses photoconductive imaging members containing a supporting substrate, certain azo pigments as photogenerating materials, and a hole transport layer that preferably contains an aryl diamine compound dispersed in certain inactive resinous binder.
Documents illustrating layered organic electrophotographic photoconductor elements with azo, bisazo, and related compounds with hole transports and certain binders that are believed to require the use of toxic solvents like methylene chloride for their preparation include U.S. Pat. Nos. 4,390,611, 4,551,404, 4,596,754, 4,400,455, 4,390,608, 4,327,168, 4,299,896, 4,314,015, 4,486,522, 4,486,519, 4,555,667, 4,440,845, 4,486,800, 4,309,611, 4,418,133, 4,293,628, 4,427,753, 4,495,264, 4,359,513, 3,898,084, 4,830,944 and 4,820,602.